To ensure safety and efficiency of transportation, the traffic must be organized, especially in cities and towns where there is large volume of traffic needs. The control of traffic at intersections, where two or more roads either meet or cross, is essential to the organization of traffic in populated areas. The control is usually achieved by a signal-controlled system to allocate the time to indicate which traffic is allowed to proceed using traffic signals, usually electric. The performance of such system is responsible for the safety and efficiency of traffic in cities and towns.
FIG. 1 shows a traditional traffic allocation system 100. As shown in FIG. 1, when two roads AB and XY intersect, traffic needs to be controlled along four directions: AB, BA, XY, and YX. For each traffic direction, there are both through traffic and turn traffic (including left turn, right turn, and U turn). Thus, for two four-lane roads, AB and XY, with two lanes at each direction crossing at an intersection, the traditional system 100 allocates through traffic and right turn traffic to the curb lane using a through and right turn traffic marking 102, and through traffic and left turn traffic to the inner lane using a through and left turn traffic marking 104.
In addition to the allocation of space in terms of lanes, FIG. 2 shows an allocation of passing permit in the AB and XY intersection. As shown in FIG. 2, the traditional system uses four phases to direct the traffic movement in the intersection. Each traffic signal is represented by a number of letters and numbers, from left to right. The first letter (A, B, X, Y) represents the road on which the traffic signal controls the traffic movement. The second number indicates a traffic pattern, with number one (“1”) indicating a through traffic, and number two (“2”) indicating various turn traffics. The third letter, which follows the number (e.g., 2), further indicates the direction of the turn traffic, with U meaning U turn, L meaning left turn, and R meaning right turn. For example, A1 controls the through traffic on Road A, and X2L controls the left turn traffic on Road X.
There are 4 phases of traffic passing permit as shown in FIG. 2. During the first phase, the lights controlling the various traffics from Road A (A1, A2U, A2L, A2R) are green and other lights are red. During the second phase, the lights controlling the various traffics from Road B (B1, B2U, B2L, B2R) are green and other lights are red. During the third phase, the lights controlling the various traffics from Road X (X1, X2U, X2L, X2R) are green and other lights are red. During the fourth phase, the lights controlling the various traffics from Road Y (Y1, Y2U, Y2L, Y2R) are green and other lights are red. FIGS. 3-6 illustrate traffic movements corresponding to the various phases. Although the U turn traffic is also included in FIG. 2, U turn traffic is in general not permitted in a two-lane setting and is thus omitted in FIGS. 3-6.
FIG. 3 illustrates the traffic movements in the first phase of the traditional system, including pedestrian traffic 108, vehicle through traffic 110, vehicle right turn traffic 112, and vehicle left turn traffic 114. A1, A2, B1, B2, X1, X2, Y1, and Y2 are the traffic lights in the system for corresponding lanes. All the vehicle traffics on Road A, including the through traffic 110, and turn traffic 112 and 114, are permitted to proceed, while no vehicle is permitted to pass through the intersection from other roads. The pedestrian traffics 108 on both Roads AB and XY are possible but limited to half of the pedestrian crossing line 106 and the pedestrians are forced to stop in the middle of the cross line to avoid conflict with passing vehicles. Traffic accident is likely to occur if pedestrian proceeds into the vehicle pathway 112 or 114. Thus, both the pedestrian and the driver in the turning vehicle would have to reduce their speed to observe other traffics to avoid accident. In some jurisdictions, vehicles on Road B, X and Y are allowed to turn right even under the red light, further increasing the risk of collision between vehicles and pedestrians.
FIG. 4 illustrates the traffic movements in the second phase of the traditional system, including pedestrian traffic 108, vehicle through traffic 110, vehicle right turn traffic 112, and vehicle left turn traffic 114. All the vehicle traffic on Road B, including the through traffic 110 and turn traffic 112 and 114, are permitted to proceed, while no vehicle is permitted to pass through the intersection from other roads. The pedestrian traffics 108 on both Roads AB and XY are possible but limited to half of the pedestrian crossing lines 106 and the pedestrians are forced to stop in the middle of the cross line to avoid conflict with passing vehicles. Traffic accident is likely to occur if pedestrian proceeds into the vehicle pathway 112 or 114. Thus, both the pedestrian and the driver in the turning vehicle would have to reduce their speed to observe other traffics to avoid accident. In some jurisdictions, vehicles on Road A, X and Y are allowed to turn right even under the red light, further increasing the risk of collision between vehicle and pedestrian.
FIG. 5 illustrates the traffic movements in the third phase of the traditional system, including pedestrian traffic 108, vehicle through traffic 110, vehicle right turn traffic 112, and vehicle left turn traffic 114. All the vehicle traffics on Road X, including the through traffic 110 and turn traffic 112 and 114, are permitted to proceed, while no vehicle is permitted to pass through the intersection from other roads. The pedestrian traffics 108 on both Roads AB and XY are possible but limited to half of the pedestrian crossing lines 106 and the pedestrians are forced to stop in the middle of the cross lines to avoid conflict with passing vehicles. Traffic accident is likely to occur if pedestrian proceeds into the vehicle pathway 112 or 114. Thus, both the pedestrian and the driver in the turning vehicle would have to reduce their speed to observe other traffics to avoid accident. In some jurisdictions, vehicles on Road A, B and Y are allowed to turn right even under the red light, further increasing the risk of collision between vehicle and pedestrian.
FIG. 6 illustrates the traffic movements in the fourth phase of the traditional system, including pedestrian traffic 108, vehicle through traffic 110, vehicle right turn traffic 112, and vehicle left turn traffic 114. All the vehicle traffics on Road Y, including the through traffic 110, and turn traffic 112 and 114, are permitted to proceed, while no vehicle is permitted to pass through the intersection from other roads. The pedestrian traffics 108 on both Roads AB and XY are possible but limited to half of the pedestrian crossing lines 106 and the pedestrians are forced to stop in the middle of the cross line to avoid conflict with passing vehicles. Traffic accident is likely to occur if pedestrian proceeds into the vehicle pathway 112 or 114. Thus, both the pedestrian and the driver in the turning vehicle would have to reduce their speed to observe other traffics to avoid accident. Therefore, there are conflicts in all of the four phases of traffic movements.
FIG. 7 illustrates another traditional traffic system 200. As shown in FIG. 7, Road AB is now an eight-lane road, with four lanes for each direction. The curb lane (the right lane) is used for right turn traffic with a right turn marking 116; the innermost lane is used for left turn and U turn with a left and U turn marking 120; and the two inner lanes between the curb lane and innermost lane are used for through traffic with a through traffic markings 118. That is, if there are three or more lanes (Road AB), left turn traffic may take the left lane, right turn traffic may take the right lane, and through traffic may take the middle lane(s). For a two-lane road, U turn traffic is generally not permitted.
The same problems of traffic movement conflicts as previously described similarly exist in the traditional system 200 as shown in FIG. 7. For example, when the traffic on Road A is permitted to proceed, the through traffic, left turn traffic, right turn traffic, and U turn traffic are permitted to proceed, while no vehicle is permitted to pass through the intersection from other roads. The pedestrian traffics on both Road AB are possible but limited to half of the pedestrian crossing lines 106 and the pedestrians are forced to stop in the middle of the cross lines to avoid conflict with passing vehicles. Similarly, traffics on Road B, X, and Y are having the same traffic conflicts.
Therefore, as described in the preceding paragraphs, the traditional traffic allocation system is both unsafe and inefficient enough. Because pedestrians cross the road while vehicle traffics, including turn traffics, proceed, it is likely that pedestrian and vehicle traffic could enter the same space at the same time to cause collision. Both pedestrian and vehicles in the intersection are required to reduce their speed to observe other traffics to avoid accident. Lower speed in passing the intersection reduces the efficiency of the whole traffic system. In addition, U turn in the system is sometimes not allowed because it would significantly increase the risk of traffic accident.
The present system of “Red/Green/Yellow” signal combination is not a perfect traffic control method as it may result in many accidents, especially during the signal change interval from yellow and following all-red periods.
In the United States and most countries, the sequence of traffic signal is red, green, and yellow. Generally, at the end of green light time, vehicles are more likely to proceed as a free flow, which means vehicles are often moving at high speed. Inevitably, when the signal of yellow light is starting, vehicle drivers often have a special difficulty, particularly at intersections of arterial roads where speed limit may be as high as 50 mph. Drivers may experience uncertainty to make a proper decision: while to continue proceeding may result a red-light running, yet at the same time it is also difficult to stop properly because an abrupt stop may cause rear-end crashes. This special difficulty is known as “dilemma zone” problem.
The Institute of Transportation Engineers (ITE) handbook defines a “dilemma zone” as a range, in which a vehicle approaching the intersection during the interval of yellow light can neither safely clear the intersection, nor stop comfortably behind the stop-line. According to information provided by Federal Highway Administration (FHWA), research has found that more than 50% of red-light violations happen within the first 0.5-seconds of the red signal indication and 94.2% of red-light violations occur within the 2.0-seconds of the red-light onset. It can be convincingly reasoned that among in all violations of red light, deliberate violations of red light (after 2 seconds of red-light onset) only accounts a tiny percentage hence almost all red-light violations would be entirely avoided if the dilemma zone problem could be satisfactorily solved.
From the view of logic, both the signal of a green light and the signal of a red light could be easily defined and have been strictly defined: a green light is a signal of “Yes” and a red light is a signal of “No”. In our daily life, the signal of a green light (or a red light) provides specific and clear instruction: a green light is a signal that means “traffic may proceed” and a red light is a signal that means “traffic may not proceed”.
However, from the view of logic, a yellow light is neither a signal of “Yes” nor a signal of “No”. Indeed a yellow light cannot be defined by one single word. At present, a yellow light can only provide general and fuzzy suggestions: a yellow light warns that the signal is about to change to red and according to the law, in the interval of yellow light, if the vehicles are in the intersection, drivers should continue moving and clear the junction safely but if they are not in the intersection, they can come to a safe stop. Therefore, when a yellow light starts, drivers must make their own decision of whether to stop or not based their own judgment. It can be convincingly concluded that a yellow light is not is a strict signal of specific instructions, rather, it is a signal of general suggestions or warnings.
In the United States, the law as stated in the Universal Vehicle Code (UVC) and Manual on Uniform Traffic Control Devices (MUTCD) is considered a Permissive yellow rule, that the driver can enter the intersection during the entire yellow interval and be in the intersection during the red indication as long as the driver entered the intersection during the yellow interval. In the United States, most states adopt Permissive yellow rule that violation only occurs if driver enters intersection after onset of red. Some states adopt Restrictive yellow rule that driver can neither enter nor be in intersection on red hence violation occurs if driver has not cleared intersection after onset of red.
The fundamental difference between Permissive yellow rule and Restrictive yellow rule could be summarized best as different priority of safety concern. While the Restrictive yellow rule emphasizes to reduce the possibility of red-light running, the Permissive yellow rule emphasizes to reduce the possibility of rear-end collisions. However, since the dilemma zone problem has two main safety issues of both red-light running and rear-end collisions, then neither Permissive yellow rule nor Restrictive yellow rule could satisfactorily solve the dilemma zone problem.
Research suggests that both the location and length of the dilemma zone is a dynamic range and may vary with the complex interactions between the response of drivers, the duration of yellow interval, traffic speeds, deceleration and acceleration rate, condition of pavement and intersection geometry, etc. Briefly, different drivers may experience different feeling of the location and length of the dilemma zone.
At present, there are two common practices aimed to mitigate the problem of dilemma zone. The first practice is to extend the length of yellow interval. The second practice is to extend the length of all red period. In real life, the mitigation effect of a prolonged yellow interval is very limited because a prolonged yellow interval often has been seemed as the extension of green light signal by many drivers. Similarly, possibility of speeding at the last second of yellow interval increases if drivers have learned that there is a prolonged all red period.
There are two main reasons why a prolonged yellow interval or all red period could not satisfactorily solve the problem of dilemma zone: (1), at present, when vehicle drivers feel they are in the location of dilemma zone, there is no assistance available to help them make a proper decision; (2), after the onset of yellow light, vehicles are still allowed to enter the dilemma zone. If an extended yellow light time cannot stop vehicles from entering the dilemma zone, then these new coming vehicles will still be involved the problem of dilemma zone, especially if these vehicles are still moving at high speed.
In some other countries, a green light flashes at the last several seconds of a green interval to provide warning of signal change in advance. In the United States, this treatment had been experimented by several states but the performance was not satisfying. Statistics suggest that drivers are more likely to speed up when a green light flashes hence the possibility of crashes is actually increasing. FHWA has made an official decision to stop further experiments on a flashing green light in the United States.
In real life, there are various road types with different positioning, different standards in design and different strategy in operation. An arterial road is a high-capacity urban road, which stands an intermediate position between freeways and collector/distributor roads in the hierarchy. In metro areas, arterial roads or major roads occupy a key position in the ground transportation system. If arterial & major roads are not effectively organized and efficiently operated, the performance of both freeway network and collector/distributor roads will be affected negatively and the whole ground transportation network may suffer speed and traffic capacity loss.
An arterial road is designed to deliver traffic at a level of service (LOS) as high as possible and the speed limits on an arterial road are typically between 50 and 80 km/h, much higher than those on collector/distributor roads. However, at present, at rush hours the LOS of an arterial road may often fall rapidly and the operating speed may be below 30 km/h or even below 20 km/h, which means an arterial road has failed to meet its positioning.
Arterial traffic is substantially different from ordinary collector/distributor roads. To increase traffic flow and speed, the numbers of intersections of arterial roads are often reduced and as a result, the average distance between two intersections on an arterial road is much longer compared to the average distance between two intersections on ordinary collector/distributor roads. It is desirable for an arterial road to be organized and operated like a freeway; not like an ordinary collector/distributor road. However, at present it is common that an arterial road is usually organized or signalized in the exact same way as an ordinary collector/distributor road.
At present, although a lane control light system may be adopted at some arterial roads, generally the performance is not satisfying. The present lane control light system consists of a downward green arrow, a red cross, and a yellow arrow. At present, a stop and queue signal such as a downward red arrow is not integrated as a part of the lane control light system.
A red cross is very different from a plain red light at signalized intersections or crosswalks. Normally, vehicles are required to stop and queue when a plain red light is on, which suggests to deny vehicles proceeding for a short period. By contrast, a red cross suggests to deny vehicles proceeding for a long time, such as hours, hence vehicles are required to use other lane(s) at the signal of a red cross. Vehicles are not suggested to, indeed required not to, queue at the signal of a red cross because normally there is no stop line at all.
The missing of a downward red arrow in a lane control light system is a serious deficiency. It means an extreme important function in traffic control, to stop vehicles of one or more lanes for a short period, is also missing accordingly. At present, a downward red arrow is missing because there is no stop line in the corresponding lane markings at all. A stop line is missing in the corresponding lane markings because drivers would be confused by a stop line if the lane control light is off: as a part of lane marking, a stop line is permanently on while a lane control light system may be on or off. The same problem also occurs at freeways, tunnels, and bridges.
FIG. 18 illustrates a traditional arterial road organization. As shown in FIG. 18, when the traffic on roads X and Y are stopped during a red light at an intersection, all the vehicles are stopped behind the stop line (SL). All vehicles have to queue behind the stop line until the traffic along the roads X and Y resumed. If a number of vehicles arrived at the intersection during the red light interval, vehicles often have difficulty making a lane change after the red light interval, although the green light signal is already on. This is because that it is difficult to find a space to make a lane change since there are continuous vehicles moving at the neighbor lanes. The lane change becomes increasingly difficult with increasing number of more lanes.
FIG. 19 illustrates the traffic weavings on a road with traditional road organization. As shown in FIG. 19, after the traffic along the roads X and Y is resumed, vehicles may change lanes, causing traffic weavings (W). Substantial traffic efficiency/capacity green light time may be lost. Traffic weavings may also significantly increase the risk of collisions. Thus, if an arterial road is organized and signalized as an ordinary collector/distributor road, the risk to road safety may be increased and the traffic capacity may be lost. The problem may be particularly pronounced during rush hour, when a large numbers of vehicles arrive at the intersection. The similar problem may also occur at a controlled/signalized crosswalk.
At signalized intersection, when a green light is on, it often takes substantial “response time” for vehicles to reach a relatively high speed, starting to accelerate from unmoving status. Normally, the first four or five vehicles take relatively long response time, and then the vehicles behind them may start to move as a relatively free flow.
In the traditional road organization system, pedestrians share the green light time with turning vehicles. FIGS. 20 to 22 illustrate traffic movements in three phases of traffic passing permit in a T section in a traditional road system. FIG. 20 illustrates the traffic movements in the first phase of the traditional system 2000, including pedestrian traffic 2002, vehicle through traffic 2004, vehicle right turn traffic 2006, bicycle through traffic 2008, and bicycle right turn traffic 2010. All the vehicle traffics on road Y, including the through traffic 2004, and turn traffic 2006, are permitted to proceed, while no vehicle is permitted to pass through the intersection from other roads. The pedestrian traffics 2002 on roads AB are possible but limited to half of the pedestrian crossing line 2012 and the pedestrians are forced to stop in the middle of the cross line to avoid conflict with passing vehicles and bicycle. Traffic accident is likely to occur if the pedestrian proceeds into the vehicle pathway 2006 and/or the bicycle pathway 2010. Thus, the pedestrian, the driver in the turning vehicle, and the turning cyclist would have to reduce their speed to observe other traffics to avoid accident. In some jurisdictions, vehicles and bicycles on Road B are allowed to turn right even under the red light, further increasing the risk of collision between vehicles and pedestrians.
FIG. 21 illustrates the traffic movements in the second phase of the traditional system 2000, including pedestrian traffic 2002, vehicle through traffic 2004, vehicle left turn traffic 2114, and bicycle through traffic 2008. All the vehicle traffics on road X, including the through traffic 2004, and turn traffic 2114, are permitted to proceed, while no vehicle is permitted to pass through the intersection from other roads. The pedestrian traffics 2002 on roads AB are possible but limited to half of the pedestrian crossing line 2012 and the pedestrians are forced to stop in the middle of the cross line to avoid conflict with passing vehicles and bicycle. Traffic accident is likely to occur if the pedestrian proceeds into the vehicle pathway 2114. Thus, the pedestrian and the driver in the turning vehicle would have to reduce their speed to observe other traffics to avoid accident. The cyclist on road X is not allowed to make a left turn as such a turn would interfere with the traffic 2004. In some jurisdictions, vehicles and bicycles on Road B are allowed to turn right even under the red light, further increasing the risk of collision between vehicles and pedestrians.
FIG. 22 illustrates traffic movements in the third phase of the traditional system 2000, including pedestrian traffic 2216, vehicle right turn traffic 2218, vehicle left turn traffic 2220, bicycle through traffic 2008, and bicycle right turn traffic 2222. All the vehicle traffics on road B, including the right turn traffic 2218, and left turn traffic 2220, are permitted to proceed, while no vehicle is permitted to pass through the intersection from other roads. The pedestrian traffics 2216 on roads XY are possible but limited to half of the pedestrian crossing line 2224 and the pedestrians are forced to stop in the middle of the cross line to avoid conflict with passing vehicles and bicycle. Traffic accident is likely to occur if the pedestrian proceeds into the vehicle pathway 2218 or bicycle pathway 2222. Thus, the pedestrian, the driver in the turning vehicle and the turning cyclist would have to reduce their speed to observe other traffics to avoid accident. In some jurisdictions, vehicles and bicycles on road Y are allowed to turn right even under the red light, further increasing the risk of collision between vehicles and pedestrians.
The disclosed systems and methods are directed at solving one or more problems set forth above and other problems.